Efficient removal of heavy metal ions with EDTA. functionalized chitosan/polyacrylamide double network

Transcription

1 Supporting Information Efficient removal of heavy metal ions with EDTA functionalized chitosan/polyacrylamide double network hydrogel Jianhong Ma a,b, Guiyin Zhou c, Lin Chu c, Yutang Liu a,b, *, Chengbin Liu c, Shenglian Luo c, Yuanfeng Wei c a College of Environmental Science and Engineering, Hunan University, Lushan South Road, Yuelu District, Changsha , P. R. China b Key Laboratory of Environmental Biology and Pollution Control (Hunan University), Ministry of Education, Lushan South Road, Yuelu District, Changsha , P.R. China c State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Lushan South Road, Yuelu District, Changsha , P. R. China Corresponding author College of Environmental Science and Engineering, Hunan University, Lushan South Road, Yuelu District, Changsha , P. R. China Tel./Fax: address: yt_liu@hnu.edu.cn (Y. Liu) Number of pages: 14 (including cover page); Number of figures: 3; Number of tables: 3. S1

2 Determination of carboxyl content. The amount of carboxyl groups immobilized was measured through the back titration method mg of each sample was mixed with 50 ml of NaHCO M solution which is standardized by 0.12 M HCl standard solution. After stirring for 20 h, the mixture was separated by filtration and the obtained filter liquor was titrated with M HCl standard solution. Afterwards, the carboxyl groups concentration was determined from the consumed HCl volume at equivalence point. The experimental results are reported on Table S1. Carboxyl groups percentage of these two gels can be calculated by: P COOH = ( M M ) V / W % 1 2 (1) Where M 1 is the concentration of prepared NaHCO 3 solution, M 2 is the filtrate concentration of NaHCO 3 solution after the interaction with gel samples, V is the volume of NaHCO 3 solution interact with gel samples. Based on the experimental results, carboxyl groups percentage of pristine CTS/PAM gel and CTS/PAM gel were calculated as 0.54 and 5.4, respectively. Representing the large number of carboxylic groups on the CTS/PAM gel surface after modified by EDTA. S2

3 Kinetic models. The pseudo-first and pseudo-second order models are usually used to describe the experimental adsorption kinetic data. Pseudo-first-order model: ( 1 ( kt) ) q = q exp t e 1 (2) Pseudo-second-order model: q t = q e qek 2t (3) where q e (mg/g) is the sorbed metal quantity at equilibrium; q t (mg/g) is the sorbed quantity at time t; k 1 (L/min) and k 2 (g/(mg min)) are the first and second order equilibrium rate constants, respectively. S3

4 Adsorption models and thermodynamics. The Langmuir isotherm often describes an ideal and theoretic adsorption process and applicable to a homogeneous adsorption surface that with an equal adsorbate affinity of all the adsorption sites, while the Freundlich isotherm model assumes heterogeneous adsorption surfaces. The Langmuir and Freundlich mathematical forms can be described as the following non-linear equation (4) and (5), respectively: q e q K C 1 + K C m L e = (4) L e q e = K C (5) F 1 n e where C e (mg/l) is the equilibrium concentration of metal ions, q e (mg/g) is the equilibrium sorption capacity, q m (mg/g) is the maximum monolayer metal ions coverage capacity per unit weight of adsorbent, K L (L/mg) and K F (mg 1-n L n /g) are the corresponding adsorption equilibrium constants, n is the adsorption intensity. The Dubinin-Radushkevish (D-R) isotherm is applied to estimate the adsorption energy. It is often expressed as: 2 ( kε ) qe = q m exp (6) ε 1 RT ln 1 + C = e E = ( 2k) 1 2 (7) (8) where q m (mol/g) is the D-R maximum adsorption capacity, k (mol 2 /kj 2 ) is the constant related to the adsorption energy, the Polanyi sorption potential ε (J/mol) is the amount of energy required to pull adsorbed molecule from its sorption site and E is the free energy (kj/mol). S4

5 Thermodynamic parameters such as free energy change ( G 0 ), enthalpy change ( H 0 ) and entropy change ( S 0 ) were calculated as follows: G = H S (9) G = (10) = (11) = (12) where K c is the equilibrium constant; C Ac and C e are equilibrium concentrations (mg/l) of heavy metal ions on the sorbent and in the solution, respectively; T is the absolute temperature (K) and R is the universal gas constant. S5

6 Selective adsorption: The selectivity of CTS/PAM gel for Cu(II) over other metal ions can be appraised by the selectivity coefficient (Cu(II)/ M(II)), which is expressed as 2 : ( ) ( ) = ( ) (13) ( ) = (14) where D Cu(II) and D M(II) are the distribution ratios (D) of the Cu(II) and other coexisted metal ions, respectively; C 0 (mg/l) and C e (mg/l) are the concentrations of metal ions before and after adsorption, respectively; V (L) is the volume of solution and W (g) is the mass of gel. S6

7 Absorbance (a) Acrylamide CTS/PAM gel Wavelength (nm) Transmitance (%) (b) CTS 3181 pristine gel gel Wavenumbers (cm -1 ) Weight (%) (c) ug/min CTS/PAM gel pristine CTS/PAM gel Temperature ( C) Temperature ( C) Figure S1. (a) The UV-vis spectra, (b) FTIR spectra of the CTS, pristine CTS/PAM gel and CTS/PAM gel, (c) TGA curves of pristine CTS/PAM gel and CTS/PAM gel (inset is the DTG curves). S7

8 Removal Efficiency (%)96 K Na Mg Ca (a) Cations/Cd(II) ratio (mol/mol) Removal Efficiency (%) K Na Mg Ca (b) Cations/Pb(II) ratio (mol/mol) Removal Efficiency (%) 96 (c) K Na Mg Ca Cations/Cu(II) ratio (mol/mol) Figure S2. Effect of cations strength on (a) Cd (II) (ph = 6, C 0 = 40 mg/l), (b) Pb (II) (ph = 5, C 0 = 80 mg/l) and (c) Cu (II) (ph = 5, C 0 = 45 mg/l) sorption on CTS/PAM gel, T = 298 K, t contact = 6 h, m/v = 1 g/l. S8

9 q e (mg/g) x10 8 4x10 8 5x10 8 6x10 8 ε 2 (a) q e (mg/g) (b) 4.0x x x10 8 ε (c) 80 q e (mg/g) x x x x10 8 ε 2 Figure S3. Nonlinear curves of ε 2 vs. q e for (a) Cd(II) (ph = 6.0), (b) Pb(II) (ph = 5.0) and (c) Cu(II) (ph = 5.0) sorption on CTS/PAM gel, T = 298 K, t contact = 6 h, m/v = 1 g/l. S9

10 Table S1. Experimental results of carboxyl content determination. Samples V (NaHCO3) /ml V (HCl) /ml M/(mol L -1 ) NaHCO 3 solution Pristine gel CTS/PAM gel S10

11 Table S2. Comparison of heavy metal ions sorption capacities with other sorbents. solution chemistry Q max (mg/g) Adsorbent conditions Pb(II) Cd(II) Cu(II) refs Zeolite/chitosan monoliths T = 298 K Ethylenediamine modified neutral ph chitosan microspheres Chitosan nanoparticles ph = 6.4, T = 293 K Chitosan/rectorie nano-hybrid ph = 6, T = 298 K composite microsphere Polyethylenimine-functionalized ph = 5, T = 298 K ion imprinted hydrogel EDTA functionalized magnetic ph = nanoparticle alginate hydrogel beads ph = Pollen chitosan ph = 5.35 for Cd, ph = microcapsules 5.18 for Cu, T = 298 K CTS/PAM gel ph = 5 for Pb and Cu, This ph = 6 for Cd, T = 298 work K S11

12 Table S3. Selective adsorption of Pb(II), Cu(II), Cd(II), Zn(II), Mn(II), and Ni(II) on CTS/PAM gel. Metals ions Ionic charge Distribution ratio (L/g) Selectivity coefficient β Cu(II)/M(II) Cu(II) Cd(II) Pb(II) Zn(II) Ni(II) Mn(II) S12

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